At present light emitting diode units, several light emitting diodes with red light, yellow light, blue light, etc, have been developed. The light emitting diodes emit light sources with different colors by means of chosen different phosphors. For example, phosphor materials such as GaAs semiconductors and so on are mainly used to emit red light. Phosphor materials such as AlInGaP semiconductors and so on are mainly used to emit yellow light. Nitride semiconductors such as InxGayAl1-x-yN wherein 0≦x≦1 and 0≦y≦1 are mainly used to emit blue light. If a light emitting diode emitting white light can be produced, light sources with different colors can be generated as desired by simply using light filters. Therefore, industrial society makes many efforts in developing white light emitting diodes.
The current developed white light emitting diodes mainly use a light emitting diode emitting color light in conjunction with a phosphor, and white light can be generated by using the color light source to excite the phosphor substance. Compared with red and yellow light emitting diodes, a blue light emitting diode can present a luminescence with high luminance and are more widely used. For example, International Publication No. WO98/5078 discloses that white light can be generated by using a blue-emitting LES as the light source and, on the LED chip, placing a phosphor substance such as YAG:Ge phosphor substance that can absorb part of the blue light and emit yellow light. Nichia Kagaku Kogyo Kabushiki in Taiwanese Publication No. TW383508 corresponding to U.S. Pat No. 5,998,925 provides a light emitting device comprising a light emitting component and a luminescent phosphor, wherein the emitting layer of the emitting component is composed of nitride compound semiconductors and the luminescent phosphor is a garnet phosphor which contains at least one element selected from a group of Y, La, Gd and Sm and at least element selected from a group of Al, Ga and In and is cerium-activated. Therefore, white ligh emitting diode can be produced by choosing a light emitting diode with different light colors in conjugation with phosphors which can emit lights with various colors upon exciting with the light.
The above white light emitting diode devices are produced by covering element the light emitting diode chip directly with a binding agent containing specific phosphor, so that when the light emitted from the light emitting diode passes through the binding agent, the phosphor contained in the binding agent would be excited and the LED finally emits white light. However, if the LED chip is directly covered with the binding agent containing phosphor, since the covering element is not even and in different thicknesses, there is problem that the phosphor would not be evenly distributed in each part of the binding agent and it is thus possible to generate a chromatic aberration when the light passes through.
Furthermore, as each LED grain manufactured in each batch emits different wavelengths, to obtain the white light as desired, the kind of phosphor and its concentration in the binding agent should be appropriately selected depending on wavelength of the light emitting diode grain to be used, which results complex process.
Moreover, covering element the LED chip directly with the binding agent containing phosphors is defective in process due to numerous and complicated procedures in the operation.
In order to improve the above drawback of the white light diode device, the present invention achieves an even distribution of the phosphor in the binding agent by placing and clamping a light-pervious binding agent containing phosphors between two transparent sheets and thus simplifies the process.